svoid closeAllOpt(Iterable l) {
  if (l == null) ret;
  for (c : l) if (c cast AutoCloseable) pcall { close(c); }
}

svoid closeAllOpt(AutoCloseable... l) {
  if (l == null) ret;
  for (c : l) if (c cast AutoCloseable) pcall { close(c); }
}